1. Field of the Invention
This invention relates to VHF radios and more specifically to a portable VHF transceiver having an adjustable antenna.
2. Description of the Prior Art
VHF transceivers which are portable and used in land mobile services normally include a removable antenna which is normally covered by a flexible rubber or plastic material. The antenna must be tuned to the radio operating frequency to get the maximum performance from the radio. The antennas include a threaded male connector which engages a female connector or RF connector such as BNC, TNC, SMA or the like which is disposed in the radio housing. In the prior art VHF transceivers which operate in the 136 MHz to 174 MHz band using frequency modulation the antennas are sold separately and pretuned to the middle of the band or to a specific frequency by cutting to length.
Helical coil antennas are tuned by cutting the antenna length to the desired frequency. This can be done by two different methods. The first method involves the use of a cutting chart on which the antenna is placed for measuring, marked and cut to length. The other method is to us test equipment in the shop or laboratory and cut the antenna by approximations until the desired adjustment is made. In both cases, there is risk of the antenna being cut too short. If the antenna is cut too short, then a new one has to be recut. Both of these methods are impractical in the field.